In a conventional internal combustion engine, an air flow control valve called a throttle valve is disposed in a main intake pipe, and this throttle valve is on-off controlled, for example, in accordance with a displacement of an accelerator pedal and is branched downstream into branch pipes connected to cylinders.
In a control apparatus for an internal combustion engine which is known in Japanese Patent Laid Open No. Hei 1-271634 for example, in addition to the above configuration, the fuel injection volume is adjusted so as to eliminate a difference in output torque for each cylinder detected by a crank angle sensor and it is compensated in response to a pressure variation detected by an internal cylinder pressure sensor.
In the above prior art, the air passage length from the throttle valve to each cylinder is too long and there occurs a delay in a change of air volume controlled by the throttle valve, thus giving rise to a problem that it is impossible to obtain an optimum air volume for each cylinder. There also has been a problem that the branch pipes connected to cylinders are different in length and shape, thus making it impossible to distribute air uniformly to the cylinders.
Thus, since the amount of air required for each cylinder cannot fed accurately, even if the amount of fuel is controlled for each cylinder, it has so far been impossible to accurately control the output torque for each cylinder.
Due to consequent unevenness in torque for each cylinder, the output of the entire internal combustion engine is lowered and a limit has so far encountered in fuel economy improving measures or emission improving measures, such as lean burn control, ultra-lean burn control, and cylinder-direct fuel injection control.